Method for increasing color density and improving color fastness of dyed fabrics

ABSTRACT

The invention provides a method for increasing the color density of a dyed fabric material of, especially, a synthetic fiber as well as the fastness of the color to rubbing and washing. The inventive method comprising (a) pretreating the dyed fabric material with an organopolysiloxane which is an amino-modified organopolysiloxane or a dimethylpolysiloxane, and then (b) exposing the thus pretreated dyed fabric material to low temperature plasma of an inorganic gas under a reduced pressure. The inorganic gas is preferably oxygen or a gaseous mixture containing at least 10% by volume of oxygen. The color-deepening effect is particularly remarkable when the color of the dyed fabric material is black to impart increased graveness and vividness of the color.

BACKGROUND OF THE INVENTION

This is a continuation-in-part application from a copending U.S. patentapplication Ser. No. 557,667 filed Dec. 2, 1983 now abandoned.

The present invention relates to a method for increasing the colordensity of a fabric material composed of, mainly, a synthetic fiber anddyed, in particular, in black color along with the effect of improvingthe color fastness of the dyed fabric material even when the dyeing ofthe fabric material is preceded by a treatment with various kinds offabric finishing agents which may eventually have an adverse effect ofdecreasing the fastness of the color imparted to the fabric material inthe subsequent dyeing process.

In the fabric dyeing industry, it is a usual practice to undertakecertain measures for increasing the color density of the dyed fabrics toobtain a deeper color subsequent to dyeing with an object to decreasethe concentration of the dye in the dyeing bath. This problem isparticularly important in the fabric materials dyed in black in order togive an impression of a grave and vivid black color. In view of theproblem of the dyeability of the fibers, the efforts for developing amethod of deeper-colored dyeing or increasing the color density of dyedfabric materials hitherto undertaken have been mainly concentrated tothose of synthetic fibers including a method in which the surface of thefiber per se is provided with microscopically fine craters by a subtlecontrol of the spinning conditions and a method in which the surface ofthe fibers is treated with a liquid dispersion of colloidal silica todeposit the silica particles thereon which form microscopic ruggednesson the fiber surface to reduce the reflectivity of light. The formermethod of microcrater formation on the fiber surface is, however, notversatile to be applicable to any types of synthetic fibers and thelatter method of the treatment with a colloidal silica dispersion isdefective due to the poor durability of the effect obtained by thetreatment which is readily lost by laundering or other treatment afterdyeing.

Alternatively, another method has been proposed in the above describedobject in which dyed fabric materials are treated with certain kinds ofsynthetic resins such as acrylic resins, fluorocarbon resins, siliconeresins and the like to provide a coating layer on the fiber surfacewhich may alter the behavior of light in reflection on the fiber surfaceto give a viewer's visual impression of a deepened color. This methodis, however, also not free from the problem of the poor durability ofthe effect and, in addition, defective in the decreased color fastnessof the dyed fabric materials, possible influences by the types of dyesand other fabric finishing agents used in combination with the abovementioned resins and eventual shifts caused in the hues and color tonesof the dyed fabric materials.

Further, it is a very common practice that fabric materials of syntheticfibers are subjected to various types of finishing treatments includingsoft finish, hard finish, water-and/or oil-repellent finish,shrink-resistant finish, crease-resistant finish, antistatic finish andthe like according to the particular requirements for the fabricmaterials such as improvements in feeling, touch, mechanical propertiesand functions and other objects. One of the serious problems in thesefinishing treatments is the decreased color fastness or, in particular,the color fastness in washing and rubbing when a dyed fabric material issubjected to such a finishing treatment after dyeing. The grade of thecolor fastness may sometimes decrease by one to three points by such afinishing treatment of a dyed fabric material to cause a great loss inthe commercial value of the product. Therefore, the types of thefinishing agents and the procedures of the finishing treatment are undervery strict restrictions for the reason of this problem in order tominimize the decrease in the color fastness of a dyed fabric materialwith full exhibition of the desired effects by the finishing treatment.Therefore, it has been a very important problem for the engineerspertaining to the manufacture of fabric-finishing agents or the processof fabric finishing by use thereof to develop an agent or a method withwhich or in which the problem of the decreased color fastness of a dyedfabric material by a finishing treatment is solved as far as possiblealthough all of the hitherto proposed methods provide only a partialsolution of the problem to give a color fastness approximating that ofthe unfinished dyed fabric material and not to give a fastness inherentto the dye per se.

As viewed from the other side, the above described problem of thedecreased color fastness of a dyed fabric material by the finishingtreatment is a limiting factor for the selection of dyes since a dyehaving a serious drawback in this respect is, whatever excellentproperties it may have otherwise, e.g. level dyeing, not usable when thedyed fabric material is subsequently subjected to a finishing treatmentto cause a large decrease in the color fastness.

Accordingly, it has been eagerly desired to develop an effective andinexpensive method for increasing the color density of a dyed fabricmaterial as well as improving the color fastness of a dyed fabricmaterial even when the dyed fabric material is subsequently subjected toa finishing treatment by use of a variety of finishing agents currentlyon use in the fabric industry.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a noveland improved method for increasing the color density of a dyed fabricmaterial by a post-treatment subsequent to dyeing without increasing theconcentration of the dye in the dyeing bath and, in the case where thedyed fabric material is subsequently finished by use of one or more ofthe fabric finishing agents, the color fastness of the dyed fabricmaterial is not decreased by such a finishing treatment.

The method of the present invention developed as a result of theextensive investigations undertaken by the inventors comprises thesuccessive steps of (a) treating a dyed fabric material with anamino-modified organopolysiloxane or a dimethylpolysiloxane having aviscosity in the range from 10² to 10⁸ centistokes at 25° C. and (b)then subjecting the thus treated dyed fabric material to exposure to lowtemperature plasma of an inorganic gas under a pressure in the rangefrom 0.01 to 10 Torr.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic illustration of an apparatus for the lowtemperature plasma treatment in the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although the inventive method is very simple and can be performedinexpensively as is mentioned above, the method of the invention is veryeffective so that the effect of increasing the color density of a dyedfabric material by the inventive method is larger by 1.5 to 2 times thanin the conventional methods consequently contributing to 10 to 30%saving of the dye to obtain a desired color density. Further, inconnection with the decrease in the color fastness of a dyed fabricmaterial caused by a finishing treatment after dyeing, not only thedecrease in the fastness can be prevented by the treatment of theinvention but also the fastness can even be increased by one to fourpoints in comparison with the fastness without the finishing treatmentso that the selection of the dyes and the finishing agents as well asthe procedures of finishing are freed from the hitherto unavoidablelimitations to greatly contribute to the increase in the variety offabric materials with large commercial values.

In the first place, the method of the present invention is applicable toany types of fibers but the effect of the inventive method is mostremarkably exhibited when the dyed fabric material is made of asynthetic fiber such as polyester fibers, nylon fibers, acrylic fibers,polypropylene fibers, cellulose acetate fibers, polyvinyl alcohol fibersand the like and the form of the fabric material is not particularlylimitative including woven cloths, knit fabrics and non-woven fabrics aswell as threads and yarns. It is of course that these fabric materialsare made of two kinds or more of different types of fibers includingnatural fibers provided that, for example, the weight proportion of thesynthetic fibers is about 50% by weight or more. The fabric materialshould be dyed before being subjected to the method of the presentinvention and the kind of the dye used for dyeing is not particularlylimitative including any commercially available ones used for dyeingalthough it should be noted that the effect of the inventive method forincreasing the color density is most strongly exhibited when the dyedfabric material is dyed in black.

In the first step (a) of the inventive method, the dyed fabric materialis treated with an amino-modified organopolysiloxane or adimethylpolysiloxane. Various commercial products of aqueous emulsioncompositions comprising an amino-modified organopolysiloxane as thedispersant are available. The amino-modified organopolysiloxane in sucha composition is a diorganopolysiloxane having a substantially linearmolecular structure having amino-substituted alkyl groups of the formula--R--NH₂ or (2-aminoethyl)amino-substituted alkyl groups of the formula--R--NH--CH₂ CH₂ --NH₂ bonded to the silicon atoms in the molecule, inwhich R is a divalent hydrocarbon group or, in particular, an alkylenegroup such as ethylene, propylene and the like. The diorgnopolysiloxaneshould contain preferably from 0.05 to 10% by moles of the abovementioned amino-substituted groups based on the overall organic groupsbonded to the silicon atoms and at least 60% by moles of the organicgroups other than the above mentioned amino-substituted groups shouldpreferably be methyl groups. The organic groups other than methyl andamino-substituted alkyl groups are exemplified by alkyl groups such asethyl and propyl groups, halogenated alkyl groups such as chloromethyl,chloropropyl and trifluoropropyl groups, unsaturation-containing groupssuch as vinyl, allyl, acryloxypropyl and methacryloxypropyl groups,epoxy-substituted groups such as 3-glycidyloxypropyl group, aryl groupssuch as phenyl group and alkoxy groups such as methoxy, ethoxy andpropoxy groups. The above defined amino-substituted diorganopolysiloxaneis particularly suitable as the pretreatment agent of the fabricmaterial and capable of giving a finished fabric product imparted with agood balance of the color density or color thickness and the feeling ortouch of the material.

Alternatively, the pretreatment agent used in the step (a) of theinventive method may be a dimethylpolysiloxane having a viscosity,preferably, in the range from 10² to 10⁸ or, more preferably, at least10³ centistokes at 25° C. in order to obtain a full effect ofcolor-deepening in the inventive method. Preferably, the pretreatmentagnet should be an aqueous emulsion containing such adimethylpolysiloxane as the dispersant. It is not always necessary thatthe organic groups bonded to the silicon atoms in thedimethylpolysiloxane are limited to methyl groups provided that themolar content of other organic groups does not exceed 20%. The organicgroups other than methyl are exemplified by those groups given as theexemplification of the organic groups other than the amino-substitutedalkyl and methyl groups in the amino-substituted diorganopolysiloxane.It is preferable that the molecules of the dimethylpolysiloxane, whichhave a substantially linear molecular structure, are trminated at bothmolecular chain ends each with a silanolic hydroxy group bonded to theterminal silicon atom.

The process for the treatment of a fabric material with the abovedescribed pretreatment agent is well known in the art of fabricprocessing including the method of dipping, padding, roll-coating,spraying and the like followed by a post-treatment of soaping, rinsingwith hot water, etc. and drying. The amount of the pretretment agentdeposited on the fabric material in this pretreatment is usually in therange from 10⁻³ to 10⁻² g/g of the fabric material.

It is of course optional that the pretreatment agent, of which theprincipal ingredient is the above described organopolysiloxane compound,may be admixed with a relatively small amount of other resinousfabric-finishing agents such as urethane resins, melamine resins,fluorocarbon resins, acrylic resins, polyacrylamide resins, polyesterresins and the like as well as certain organopolysiloxane resinsmodified with polyoxyalkylene groups, epoxy groups, fluoroalkyl groupsand the like.

The fabric material pretreated in the above described manner with thepretreatment agent containing an organopolysiloxane is then subjected toa treatment with low temperature plasma in the step (b) of the inventivemethod. The procedure of the low temperature plasma treatment is alsowell known in the art. That is, the dyed fabric material under treatmentis placed inside a plasma chamber capable of being evacuated to areduced pressure and equipped with two or two sets of dischargeelectrodes, one or one set thereof being grounded and the other or theother set thereof serving as a power electrode, and low temperatureplasma is generated inside the plasma chamber by supplying an electricpower to the electrodes at a voltage of, for example, 400 volts orhigher while the atmosphere inside the plasma chamber is kept under areduced pressure with a stream of an inorganic gas.

Suitable inorganic gases to fill the plasma chamber under a reducedpressure are exemplified by helium, neon, argon, nitrogen, oxygen, air,nitrous oxide, nitrogen monoxide, nitric oxide, carbon monoxide, carbondioxide, bromine cyanide, sulfur dioxide, hydrogen sulfide and the like.These inorganic gases may be used either alone or as a mixture of twokinds or more according to need. In particular, it is preferable in theinventive method that the inorganic gas is an oxidizing gas which may beoxygen or a gaseous mixture containing at least 10% by volume of oxygen.

The pressure of the gaseous atmosphere inside the plasma chamber ispreferably in the range from 0.01 to 10 Torr. Low temperature plasma isreadily generated with stability by the glow discharge in the atmosphereunder a pressure in this range by supplying an electric power of, forexample, 10 watts to 100 kilowatts at a frequency of 10 kHz to 100 MHzbetween the electrodes installed inside the plasma chamber although thefrequency is not particularly limited to the above mentioned highfrequency range but may be direct current, low frequency or a frequencyof microwave range. The electrodes are not necessarily installed insidethe plasma chamber but may be installed outside the plasma chamber ormay be replaced with a single work coil for high frequency surroundingthe plasma chamber although installation of the discharge electrodesinside the plasma chamber is preferable from the standpoint of obtainingeffective results of the low temperature plasma treatment. Theseelectrodes are connected to the power source, e.g. high frequencygenerator, either by capacitive coupling or by inductive coupling.

The forms of the electrodes are also not particularly limitative and thepower electrode and the grounded electrode may be of the same form ordifferent forms from each other. Plate-like, ring-like, rod-like andcylindrical electrodes are equally suitable though dependent on theparticular requirements. A convenient design of the discharge electrodesis that the walls of the plasma chamber are made of a metal to serve asa grounded electrode and a power electrode of a suitable form isinstalled inside the plasma chamber as insulated from the walls.Assuming that the electrodes are installed inside the plasma chamber,the distance between the grounded and power electrodes is preferably inthe range from 1 to 30 cm or, more preferably, from 2 to 10 cm in orderto obtain higher efficiency of the treatment.

The material of the electrodes should of course be conductive andcopper, iron, stainless steel, aluminum and the like metals are suitableas the material of the electrodes. In order to ensure stability of thedischarge between the electrodes, it is preferable that the surface ofthe electrodes or, in particular, the power electrode is provided with aheat-resistant and electrically insulating coating layer of, forexample, porcelain enamel, glass or ceramic having a dielectric strengthor breakdown voltage of, desirably, at least 1000 volts/mm.

In the following, examples are given to illustrate the inventive methodand the effectiveness thereof in more detail but not to limit the scopeof the invention in any way. As is understood from the examples, fabricmaterials treated according to the inventive method are imparted withremarkably deepened color with fastness so that the inventive method iseconomically very advantageous by virtue of the great saving in theamount of the dye required for obtaining a desired color density. Theadvantage is particularly great in the black dyeing of polyester fiberswhere the amount of the black dye is remarkably large when a deep blackcolor is desired.

The apparatus for the low temperature plasma treatment used in thefollowing examples is illustrated in the accompanying drawing. In theFIGURE, the plasma chamber 1 is made of a stainless steel and capable ofbeing evacuated by means of the vacuum pump 2 down to a pressure of 0.01Torr or below. The plasma chamber 1 is provided with a gas inlet 3through which a gas is introduced into the plasma chamber 1 toconstitute the gaseous atmosphere inside the chamber 1. The open end ofthe gas inlet 3 is branched in manifold (in three branches in theFIGURE) to ensure uniformity of the atmospheric condition inside thechamber 1. A stainless steel-made rotatable cylindrical electrode 4inside the plasma chamber 1 is supported vacuum-tightly by a faceplateof the plasma chamber 1 in a cantilever manner and driven by an electricmotor 5 installed outside the chamber 1 at a controllable velocity. Therotatable cylindrical electrode 4 is electrically grounded through thewalls of the plasma chamber 1. The temperature of the rotatablecylindrical electrode 4 can be controlled by passing a heating orcooling medium through inside. Facing the rotatable cylindricalelectrode 4, a rod-like electrode 6, which serves as a power electrode,is held in parallel to the rotating axis of the rotatable cylindricalelectrode 4 to form a gap of uniform width therebetween. The powerelectrode 6 is, of course, electrically insulated from the walls of theplasma chamber 1 and connected to the ungrounded terminal of a highfrequency generator 8. The pressure inside the plasma chamber 1 can bedetermined by means of a Pirani gauge 7 connected to the chamber 1.

In performing the low temperature plasma treatment in the abovedescribed apparatus, the efficiency of the high frequency generator wascontrolled at the maximum by changing the position of the tap in theanode coil in order to obtain matching of the impedance of theoscillator tube and the load impedance varying with various parameterssuch as the kind and pressure of the atmospheric gas, number of theelectrodes and others. In the measurement of the high frequency output,the p-p value of the output voltage was obtained by doubling the peakvalue of the output voltage determined in a circuit comprising a voltagedivider, rectifier and D.C. voltmeter. The output current was given bythe effective value determined in a circuit comprising a currenttransformer, current-voltage converter and D.C. voltmeter, of which thecurrent-voltage converter was operating to give an output of athermocouple in mV detecting the temperature elevation of a heater inproportion to the input current in the heater.

EXAMPLE 1

A georgette crepe cloth of pure polyester fiber dyed in black with 10%(o.w.f.) of Dianix Black BG-FS was treated with either one of thefollowing pretreatment agents I to VII by the padding method of 1dipping-1 nipping with a 1% aqueous solution of the pretreatment agentto give a pick-up of 103% by weight followed by drying at 105° C. for 3minutes and then curing at 180° C. for 30 seconds.

I: an aqueous emulsion containing 30% by weight of an amino-modifiedorganopolysiloxane having a viscosity of about 2000 centistokes at 25°C., of which the molar content of the amino-substituted alkyl groups was1%

II: an aqueous emulsion containing 30% by weight of an amino-modifiedorganopolysiloxane having a viscosity of about 1000 centistokes at 25°C., of which the molar content of the amino-substituted alkyl groups was0.2%

III: an aqueous emulsion containing 30% by weight of an amino-modifiedorganopolysiloxane having a viscosity of about 10⁶ centistokes at 25°C., of which the molar content of the amino-substituted alkyl groups was0.3%

IV: an aqueous emulsion containing 30% by weight of adimethylpolysiloxane having a viscosity of about 10⁶ centistokes at 25°C. and terminated at both molecular chain ends each with atrimethylsilyl group

V: an aqueous emulsion containing 30% by weight of adimethylpolysiloxane having a viscosity of about 10⁵ centistokes at 25°C. and terminated at both molecular chain ends each with adimethylhydroxysilyl group

VI: an aqueous emulsion containing 30% by weight of adimethylpolysiloxane having a viscosity of about 1000 centistokes at 25°C. and terminated at both molecular chain ends each with atrimethylsilyl group

VII: an aqueous emulsion containing 30% by weight of adimethylpolysiloxane having a viscosity of about 100 centistokes at 25°C. and terminated at both molecular chain ends each with atrimethylsilyl group

A test cloth of 30 cm by 30 cm wide taken by cutting each of the thustreated cloths and the same cloth before the treatment with thepretreatment agent was spread and fixed on the rotatable cylindricalgrounded electrode of the plasma apparatus as described before and theplasma chamber was evacuated. When the pressure inside the chamber hadreached 0.03 Torr, oxygen was continuously introduced into the chamberat a rate of 2 liters/minute so that the pressure inside the plasmachamber was maintained at 0.2 Torr by the balance of the continuousevacuation and introduction of the oxygen gas.

While keeping the atmospheric conditions as described above, lowtemperature plasma was generated inside the chamber by supplying a highfrequency electric power of 15 kilowatts at a frequency of 110 kHz tothe electrodes to expose the surface of the cloth to the atmosphere oflow temperature plasma for 60 seconds. The p-p value of the dischargevoltage was 1700 volts and the effective value of the discharge currentwas 20 amperes.

The thus plasma-treated test cloths were subjected to the evaluation ofthe color density and the washing resistance of the color as well as thecolor fastness by rubbing to give the results shown in Table 1 below.The methods for the evaluation of these items were as follows.

The color density L was calculated from the equation ##EQU1## in which Yis the reflectivity at a wavelength of 800 nm determined by use of acolor densitometer (Model Macbeth MS 2020 manufactured by Macbeth Co.).Table 1 includes the value of the relative color density or index ofeach test specimen taking the color density of the untreated cloth as100.

The washing resistance of the color of the dyed cloths was evaluated bythe determination of the value of the color density of the test clotheither before or after washing in an aqueous washing bath. The test ofaqueous washing was performed with a 2 g/liter aqueous solution of asynthetic neutral detergent in a bath ratio of 1:30, in which the testcloth was shaken for 10 minutes at 40° C. followed by rinse anddehydration. This cycle of washing, rinse and dehydration was repeated10 times.

The evaluation of the color fastness to rubbing was performed accordingto the procedure specified in JIS L 0849 for a test cloth in both dryand wet conditions under a load of 200 g by repeating 100 times ofreciprocative rubbing movements.

                  TABLE 1                                                         ______________________________________                                                  Color density, L-value                                              Pre-      (index)          Color fastness to                                  treat-    Plasma treatment rubbing (dry/wet)                                  ment         Before   After    Plasma treatment                               agent     No     washing  washing                                                                              No     Yes                                   ______________________________________                                        Exam- ple 1                                                                         None    14.4 (100)                                                                           13.5 (107)                                                                           13.8 (108)                                                                            ##STR1##                                                                             ##STR2##                                 I       14.1 (104)                                                                            7.0 (247)                                                                            9.6 (198)                                                                            ##STR3##                                                                             ##STR4##                                 II      12.7 (122)                                                                            9.9 (164)                                                                           11.8 (160)                                                                            ##STR5##                                                                             ##STR6##                                 III     14.0 (106)                                                                            7.9 (206)                                                                           10.9  (184)                                                                           ##STR7##                                                                             ##STR8##                                 IV      14.4 (100)                                                                            6.7 (243)                                                                            8.1 (200)                                                                            ##STR9##                                                                             ##STR10##                                V       14.2 (103)                                                                            6.1 (261)                                                                            7.5 (212)                                                                            ##STR11##                                                                            ##STR12##                                VI      14.3 (103)                                                                            7.2 (236)                                                                            8.4 (190)                                                                            ##STR13##                                                                            ##STR14##                                VII     14.3  (99)                                                                            8.2 (208)                                                                            9.6 (178)                                                                            ##STR15##                                                                            ##STR16##                          Exam- ple 2                                                                         None    16.4 (100)                                                                            15.1 (112)                                                                          15.4 (108)                                                                            ##STR17##                                                                            ##STR18##                                I       15.6 (108)                                                                           11.8 (160)                                                                           12.4 (150)                                                                            ##STR19##                                                                            ##STR20##                                II      14.4 (120)                                                                           13.2 (141)                                                                           14.7 (134)                                                                            ##STR21##                                                                            ##STR22##                                III     15.5 (107)                                                                           12.5 (152)                                                                           13.2 (143)                                                                            ##STR23##                                                                            ##STR24##                                IV      14.9 (116)                                                                           10.8 (180)                                                                           12.2 (158)                                                                            ##STR25##                                                                            ##STR26##                                V       14.8 (115)                                                                           10.3 (185)                                                                           11.7 (162)                                                                            ##STR27##                                                                            ##STR28##                                VI      14.8 (115)                                                                           11.7 (172)                                                                           12.5 (152)                                                                            ##STR29##                                                                            ##STR30##                                VII     14.9 (116)                                                                           11.8 (164)                                                                           12.8 (146)                                                                            ##STR31##                                                                            ##STR32##                          ______________________________________                                    

EXAMPLE 2

A woven cloth of pure polyester gaberdine cloth for black schoolboyuniform was subjected to the pretreatment with either one of thepretreatment agents I to VII described in Example 1 by the method ofpadding with 1 dipping-1 nipping with a 3% by weight aqueous solution ofeach agent to give a pick-up of 80% by weight followed by drying at 105°C. for 5 minutes and then curing at 180° C. for 30 seconds.

Each of the thus pretreated cloths as well as a cloth before thepretreatment cut in 30 cm by 30 cm wide was subjected to the lowtemperature plasma treatment in substantially the same manner as inExample 1. Thus, the plasma chamber was evacuated and, when the pressureinside the plasma chamber had reached 0.05 Torr, air was continuouslyintroduced into the chamber at a rate of 5 liters/minute so that thepressure inside the plasma chamber was maintained at 0.4 Torr by thebalance of the continuous evacuation and introduction of the air.

While keeping the atmospheric conditions as described above, lowtemperature plasma was generated inside the chamber by supplying a highfrequency electric power of 20 kilowatts at a frequency of 200 kHz tothe electrodes to expose the surface of the cloth to the atmosphere oflow temperature plasma for 300 seconds. The p-p value of the dischargevoltage was 1800 volts and the effective value of the discharge currentwas 30 amperes.

The thus plasma-treated and untreated cloth specimens were subjected tothe evaluation of the color density either before or after 10 timesrepeated cycle of washing as well as color fastness to rubbing in thesame manner as in Example 1 to give the results shown in Table 1.

What is claimed is:
 1. A method for increasing the color density andcolor fastness of a dyed fabric material composed of at least 50% byweight of a synthetic fiber which comprises the steps of: (a) treating adyed fabric material with an amino-modified organopolysiloxane or adimethylpolysiloxane having a viscosity in the range from 10² to 10⁸centistokes at 25° C.; and (b) then exposing the dyed fabric material tolow temperature plasma in an atmosphere of an inorganic gas under apressure in the range from 0.01 Torr to 10 Torr.
 2. The method asclaimed in claim 1 wherein the inorganic gas is an oxidizing gas whichis oxygen or a gaseous mixture containing at least 10% by volume ofoxygen.
 3. The method as claimed in claim 1 wherein the amount ofdeposition of the amino-modified organopolysiloxane or adimethylpolysiloxane on the dyed fabric material is in the range from10⁻³ to 10⁻² g per g of the dyed fabric material.
 4. The method asclaimed in claim 1 wherein the amino-modified organopolysiloxane hasaminoalkyl groups of the formula --R--NH₂ or (2-aminoethyl)aminoalkylgroups of the formula --R--NH--CH₂ CH₂ --NH₂, in which R is an alkylenegrous, bonded to the silicon atoms in such a molar amount from 0.05 to10% of all of the organic groups bonded to the silicon atoms.